On-demand hierarchical patterning with electric fields.

We report a method to generate hierarchical topographical patterns on demand under the control of applied voltages. The method is implemented by harnessing the electro-creasing instability in multilayerelastomer films. The critical electric field for electro-creasing instability in a layer of elastomer scales with square root of the elastomer's modulus, while the wavelength of instability pattern scales with the layer's thickness. By rationally designing elastomer films with varied modulus and thickness throughout different layers, we control the formation of surface instability patterns with feature sizes of different scales under prescribed voltages. The method is very versatile, giving various types of hierarchical patterns such as randomly oriented, aligned, and gradient ones. A theoretical model is developed and validated to guide the design of hierarchical patterns.